Many consumer devices generate and utilize digital data in increasingly large quantities. Portable digital cameras for still and/or moving pictures, for example, generate large amounts of digital data representing images. Each digital image may require up to several megabytes (MB) of data storage.
One form of storage device currently used in portable devices such as digital cameras is Flash memory. Flash memory is generally mechanically robust, is low power, and has good data transfer characteristics. However, Flash memory remains relatively expensive, such as $1.50–$2 per MB. Because of the price it is generally unreasonable to use Flash memory as an archive device, thus requiring data to be transferred from it to a secondary archival storage. Also, it becomes prohibitively expensive to include a large amount of Flash memory in an inexpensive digital camera or similar digital appliance, such as an MP3 player or PDA. This can make certain features unavailable for various applications, such as recording video on an inexpensive digital camera, and can impair the function of other features, such as limiting the number of pictures a digital camera can store or the number of songs an MP3 player can store.
Magnetic “hard disc” storage is typically used for archival storage, even in portable devices. Miniature hard disc drives are available for the PCMCIA type III form factor, offering capacities of up to 4 GB. However, such disc drives are still relatively expensive at least partially because of the relatively high fixed cost of the disc controller electronics. Miniature hard drives have other disadvantages when compared to Flash memory, such as lower mechanical robustness, higher power consumption, for example about 2 to 4 W, and relatively long access times.
Removable optical storage discs can similarly be used, and offer one large advantage compared to hard disc. The removable optical media is very inexpensive, for example of the order of $0.03 per MB for Minidisc media. However in most other respects optical disc storage compares poorly with magnetic hard discs including relatively poor power consumption, mechanical robustness, bulk, and access performance.
Magnetic tape has even lower media cost than removable optical discs. However it shares other disadvantages of rotating disc storage, particularly with respect to physical bulk, and power consumption. In addition, magnetic tape has the disadvantage of serial access. This presents two additional application problems, namely very slow random access performance and restriction to uniform time compression techniques for storing video or other types of data.